1. Field of Use
This invention relates to a background screen device in color difference image composite photography or “chroma-key” still or motion photography. The invention may be used with traditional silver halide photographic imagery or with electronic digital photography. The invention also relates to a method of lighting a background screen to minimize shadows and to compress the space between the foreground photo subject and background screen.
2. Related Art
Chroma-key and “color difference”, “green screen” or “blue screen” photography are known. One limitation has been the difficulty of removing or subtracting of the background or background color from the foreground image when the background is non-uniform. The variation of the background may be caused by uneven lighting or shadows. Another problem has been “color spilling”. Another limitation has been the amount of space and cost of lighting required to achieve a sufficiently uniform background or maintain the background due to movement of the photo subjects or changes in other light sources. Several methods or devices have been used in efforts to overcome these limitations. For example U.S. Pat. Nos. 5,897,413 and 6,211,941 (Erland) teach use of a bi-axially stretchable fabric of synthetic fibers treated with a dye. The technique utilizes the photochemical properties of light to actinically energize the treated fibers for improved illumination of the background screen surface. Other methods have attempted to alter the placement of lights or light reflective surfaces.
U.S. Pat. No. 6,674,485 (Akiyama) assigned to Hitachi Software Engineering Inc., describes the chroma-keying as an image compositing method wherein a picture is taken of a subject, composting a foreground (subject) image of the picture with a background image and printing out the combined or composite image. The method comprises the steps of: extracting the foreground image from the background; memorizing saturation, brightness and hue distribution of the background image; and correcting saturation, brightness and hue distribution of the foreground image with respect to the saturation, brightness and hue distribution of the background image.
Further chromo-keying requires a blue or green screen (or other color screen as will be appreciated by persons skilled in the art) behind the foreground (photo subject) that is substantially uniform, featureless and without shadow. This requires a number of multi-directional light sources behind the subject to prevent the shadow of the subject from casting on the background screen. Accordingly chroma-keying requires considerable cost and sufficiently large space to practice due to the exacting lighting requirements needed to maintain a uniform and featureless background behind the photo subject. This has limited the applicability or utility of the method.
Frequently, the background is a colored screen is made from a woven fabric. This is an ideal material due to it being lightweight, foldable and having the ability to be cut in a variety of sizes and shapes. It also provides a good support or substrate for color coating, printing or paintings. The Hitachi invention utilizes a small and rigid LED type lighted screen behind the photo subject while the subject stands or sits in a small booth like compartment that is shielded from outside light sources. The background screen is therefore limited in size and shape and is not collapsible or lightweight.